Recent years have witnessed an increasing growth in the use of ceramic fibers for numerous types of high temperature applications. However, most commercially available refractory adhesives generally have physical and chemical properties which make them unsuitable for use with ceramic fiber products. Often, such adhesives contain binders such as inorganic silicates which can attack the ceramic fibers and/or become electrically conductive at high temperatures. Such undesirable characteristics severely limit the areas of application of such adhesives leaving alternatives which are economically unattractive. In spite of such drawbacks, the tendency for favoring inorganic adhesives may be appreciated when one has used and encountered the problems inherent with employing many of the organic adhesives at high temperatures. Carbonization and volatilization are representative of the drawbacks of such compositions. What is needed is an inorganic adhesive which is not only useful at high temperatures, but displays numerous desirable properties so as to make it suitable for a broad spectrum of applications. Such a composition should not only retain its insulating value at high temperatures, but should also be able to retain sufficient rigidity to remain in place when subject to stresses and other forces at high temperatures. It should also be inert with respect to those items which its bonds, but should be able to move with them upon thermal cycling.
Representative of the prior art in this area is U.S. Pat. No. 3,231,401, entitled "Refractory Composition" by Price et al. This patent discloses a composition formed by ball milling ceramic fibers (preferably of the aluminum silicate variety) until the fibers have a length to diameter ratio of from about 10:1 to about 50:1. The shortened fibers are then mixed with an aqueous dispersion of colloidal inorganic oxide in an amount so as to provide an oxide content of from about 3 percent to about 40 percent by weight of the mixture on a dry basis. Careful control of the length to diameter ratio is credited with any number of the composition's properties.
U.S. Pat. No. 3,758,317, "Monolithic Inorganic Structures," by Moore et al discloses a homogeneous composition of negatively charged colloidal silica particles and positively charged colloidal particles which can be combined with particulate or fibrous refractory material. A "gel-like" structure is formed which upon drying experiences shrinkage.